A
Constraints object holds the constraints that govern the way a component's size and position change in a container controlled by a
SpringLayout. A
Constraints object is like a
Rectangle, in that it has
x,
y,
width, and
height properties. In the
Constraints object, however, these properties have
Spring values instead of integers. In addition, a
Constraints object can be manipulated as four edges -- north, south, east, and west -- using the
constraint property.
The following formulas are always true for a Constraints object (here WEST and x are synonyms, as are and NORTH and y):
EAST = WEST + WIDTH
SOUTH = NORTH + HEIGHT
HORIZONTAL_CENTER = WEST + WIDTH/2
VERTICAL_CENTER = NORTH + HEIGHT/2
ABSOLUTE_BASELINE = NORTH + RELATIVE_BASELINE*
For example, if you have specified the WIDTH and WEST (X) location the EAST is calculated as WEST + WIDTH. If you instead specified the WIDTH and EAST locations the WEST (X) location is then calculated as EAST - WIDTH.
[RELATIVE_BASELINE is a private constraint that is set automatically when the SpringLayout.Constraints(Component) constructor is called or when a constraints object is registered with a SpringLayout object.]
Note: In this document, operators represent methods in the Spring class. For example, "a + b" is equal to Spring.sum(a, b) , and "a - b" is equal to Spring.sum(a, Spring.minus(b)) . See the Spring API documentation for further details of spring arithmetic.
Because a Constraints object's properties -- representing its edges, size, and location -- can all be set independently and yet are interrelated, a Constraints object can become over-constrained. For example, if the WEST, WIDTH and EAST edges are all set, steps must be taken to ensure that the first of the formulas above holds. To do this, the Constraints object throws away the least recently set constraint so as to make the formulas hold.